Wellbore annulus flushing valve

ABSTRACT

The invention relates to downhole wellbore apparatus and particularly, but not exclusively, to apparatus for use in wellbore cleaning operations. A downhole tool ( 2 ) comprises a body ( 4 ) having a bore extending longitudinally therethrough, wherein the tool ( 2 ) further comprises a one-way valve ( 24,26 ) for allowing a flow of fluid in a first direction through the tool bore and preventing a flow of fluid in a second direction through the tool bore, the second direction being opposite to the first direction. The tool further comprises means ( 38 ) for rendering the one-way valve ( 24,26 ) inoperable so as to be ineffective at preventing fluid flow; and means ( 44,40 ) for selectively making the one-way valve operable so as to be effective at allowing fluid flow in said first direction and preventing fluid flow in said second direction.

The invention relates to downhole wellbore apparatus and particularly,but not exclusively, to apparatus for use in wellbore cleaningoperations.

It is common practice in the oil and gas drilling industries toperiodically clean a wellbore so as to ensure wellbore integrity andmaximise the efficiency of oil and gas recovery operations. A techniqueused in this regard involves pumping a suitable fluid downhole throughthe annulus formed between the wellbore and downhole equipment locatedtherein. The objective of this operation is to flush unwanted debrisdown the annulus and back uphole via the interior of the downholeequipment. If considered desirable, the equipment may include a junkcatcher in which any unwanted debris flowing uphole within the equipmentmay be retained. The remaining fluid flow continues to the surface.

A problem can be encountered with the aforementioned cleaning techniquein circumstances where it is undesirable for certain materials withinthe wellbore to be brought to the surface. For example, a wellborecleaning operation will frequently be conducted in a wellbore which isnot considered live (in other words, a wellbore which is not in fluidcommunication with an oil resource). However, when the precise locationof an oil resource is not known for example, it is possible for awellbore cleaning operation to flush an unexpected mixture of drillingfluid, debris and oil uphole to the surface. This recovery of oil isundesirable and can lead to pollution of the environment.

It is an object of the present invention to improve the downhole tooltypically used in wellbore cleaning operations.

The present invention provides a downhole tool comprising a body havinga bore extending longitudinally therethrough, wherein the tool furthercomprises a one-way valve for allowing a flow of fluid in a firstdirection through the tool bore and preventing a flow of fluid in asecond direction through the tool bore, the second direction beingopposite to the first direction; means for rendering the one-way valveinoperable so as to be ineffective at preventing fluid flow; and meansfor selectively making the one-way valve operable so as to be effectiveat allowing fluid flow in said first direction and preventing fluid flowin said second direction.

Thus, a string of cleaning equipment including the downhole tool of thepresent invention can be used in a conventional way whilst the one-wayvalve is rendered inoperable. However, if undesirable materials (e.g.oil deposits) are recovered at the surface, then the means forselectively making the one-way valve operable may be activated. In thisway, the one-way valve will be subsequently capable of allowing a flowof fluid in a first direction through the tool bore whilst preventing aflow of fluid in the second direction through the tool bore. Thearrangement of the tool in the string may be such that said firstdirection is that taken by fluid flowing in a generally downholedirection. Thus, fluid flowing in the opposite direction towards thesurface will be resisted. Pollution to the environment may be therebylimited. Furthermore, when the string of equipment is removed from thewellbore, the one-way valve allows fluid to flow downwardly relative tothe equipment and drain therefrom.

Preferably, the means for rendering the one-way valve inoperablecomprises means for restricting movement of said valve. Said movementrestricting means may be movable relative to the tool body and may bebiased towards a position wherein movement of the one-way valve is notrestricted so as to render said valve inoperable. It is also preferablefor said means for selectively making the one-way valve operable tocomprise means for releasably retaining said movement restricting meansin a position wherein the one-way valve is inoperable. It isparticularly desirable for said means for releasably retaining saidmovement restricting means to comprise a shear pin securing saidmovement restricting means to the tool body.

The means for selectively making the one-way valve operable may comprisea nozzle which is mounted on said movement restricting means and ismovable between a first position, in which a flow of fluid through thebody bore is resisted by the nozzle, and a second position, in which aflow of fluid through the body bore is not resisted by the nozzle or isresisted to a lesser extent by the nozzle than when the nozzle is in thefirst position. The nozzle may also be mounted on said movementrestricting means with a pivotal connection so that the nozzle tends tobe moved to the first position by a fluid flowing through the tool borein said first direction. Preferably, means are provided for retainingthe nozzle in the second position when said movement restricting meansis in a position wherein movement of the one-way valve is not restrictedso as to render said valve inoperable.

Also, the one-way valve may comprise a closure member pivotally mountedto the tool body and movable between a first position, in which fluidwithin the body bore may flow passed the closure member, and a secondposition, in which fluid within the body bore is prevented from flowingpassed the closure member so that fluid on one side of the closuremember is isolated from fluid on an opposite side of the closure member.The closure member may be biased towards the second position.

Ideally, the means for releasably retaining said movement restrictingmeans comprises a latching means. The latching means may comprise a pinmounted to one of the tool body and movement restricting means; and agroove, for receiving the pin, mounted in the other of the tool body andmovement restricting means. The groove preferably defines a closed loop.

A second aspect of the present invention provides a downhole toolaccording to the appended independent claim 14. Further novel andadvantageous features of this tool are defined in the appended dependentclaims 15-18.

An embodiment of the present invention will now be described withreference to the accompanying drawings, in which:

FIG. 1 is a cross-sectional side view of an embodiment of the presentinvention arranged with the one-way valve rendered inoperable;

FIGS. 2 and 3 are cross-sectional side views of the embodiment of FIG. 1wherein means for selectively making the one-way valve operable is beingprogressively moved so as to make said valve operable;

FIG. 4 is a cross-sectional side view of the embodiment of FIG. 1wherein the one-way valve is operable;

FIG. 5 is a cross-sectional side view of the embodiment of FIG. 1modified with a lock mechanism wherein the one-way valve is renderedinoperable;

FIG. 6 is a cross-sectional side view of the embodiment of FIG. 5wherein the one-way valve is operable;

FIG. 7 is a cross-sectional side view of a one-way valve according tothe second aspect of the present invention;

FIG. 8 is a cross-sectional side view of the one-way valve of FIG. 7rendered inoperable;

FIG. 9 is a cross-sectional side view of the valve arranged in FIG. 7connected to the uphole end of the valve arranged in FIG. 1;

FIG. 10 is a cross-sectional side view of the valve arranged in FIG. 8connected to the uphole end of the valve arranged in FIG. 1;

FIG. 11 is a cross-sectional side view of the valve arranged in FIG. 8connected to the uphole end of the valve arranged in FIG. 4;

FIG. 12 is a cross-sectional side view of the valve shown in FIGS. 7 and8 modified so as to comprise a means for repeatedly latching the valvein operable and inoperable configurations;

FIG. 13 is a cross-sectional side view of the valve of FIG. 12 pressedby fluid flow into an inoperable configuration; and

FIG. 14 is a cross-sectional side view of the valve of FIG. 12 latchedin an inoperable configuration.

The accompanying drawings show a downhole valve 2 which comprises a body4, a one-way valve assembly 6 mounted within the body 4, and a pluralityof further components mounted within the body 4 for rendering theone-way valve assembly 6 inoperable and, as required, selectively makingthe one-way valve operable. All these components are discussed ingreater detail below.

The body 4 comprises standard uphole and downhole crossover members 8,10for allowing the downhole valve 2 to be connected to additionalequipment within a cleaning string. The uphole crossover member 8 isthreadedly connected to an uphole body component 12 and sealed therewithby means of an O-ring seal 13. The downhole crossover member 10 isthreadedly connected to a downhole body component 14. Both the upholeand downhole body components 12,14 are threadedly connected to oneanother. A leaking of fluid between the connection of the two bodycomponents 12,14 is prevented by means of an O-ring seal 16 between thetwo body components. The crossover members 8,10 and the uphole anddownhole body components 12,14 have a generally cylindrical shape and,when assembled with one another, define a generally cylindrical body 4having a bore 18 extending longitudinally therethrough. In use, wellborefluid flushed through the annulus will flow upwardly through the stringto which the valve 2 is connected and, in turn, through the bore 18 ofthe valve body 4.

The downhole end of the uphole crossover member 8 defines a downwardlyfacing annulur shoulder 20 which inwardly projects into the body bore18. An upwardly facing annular shoulder 22 having the same dimensions asthe downwardly facing shoulder 20 is defined on the uphole bodycomponent 12 in a position downhole of the downwardly facing shoulder20. A circumferential recess in the body bore 18 is thereby provided inwhich the one-way valve assembly 6 is located.

The one-way valve assembly 6 comprises two flapper cartridges 24,26located one above the other. Each flapper cartridge 24,26 comprises acylindrical body 28 having an outer cylindrical surface in contact withthe inner surface of the uphole body component 12 and sealed thereagainst with an O-ring seal 30. Each cartridge body 28 defines anannular valve seat 32 upon which a flap 34 pivotally connected to thecartridge body 28 by means of a hinge 36 may locate. Each flap 34 isbiased by means of a spring (not shown) towards a position wherein theflap 34 is engaged with the associated seat 32 so as to seal the bodybore 18. The annular surface of each valve seat 32 is downwardly facingand each flap 34 is arranged so as to be movable from the associatedvalve seat 32 against the spring bias by a fluid flowing downholethrough the body bore 18.

When the downhole valve 2 is run in hole, the one-way valve assembly 6is in an inoperable state. In other words, the flaps 34 are restrainedso that they cannot seal against the valve seat 32 and thereby preventan uphole flow of fluid through the body bore 18. As shown in each ofthe configurations of FIGS. 1 to 3, the flaps 34 are retained in aposition spaced from the valve seats 32 by means of an elongatecylindrical mandrel 38. When the downhole valve 12 is configured forrunning in hole (as shown in FIG. 1), the mandrel 38 abuts at its upholeend with the downhole end of the uphole crossover member 8 and isretained in this position relative to the body 4 by means of four shearpins 40 mounted to the downhole body component 14. The shear pins 40retain an annular block 42 in a fixed axial position on the interiorsurface of the downhole body component 14. The annular block 42 providesan upwardly facing annular surface upon which the mandrel 38 issupported.

Located between the downhole end of the mandrel 38 and the upwardlyfacing annular surface of the block 42 is a third flapper cartridge 44.This further flapper cartridge 44 is identical to the flapper cartridgesof the one-way valve assembly 6 other than in that the cartridge 44 islocated in an inverted orientation (i.e. with the annular valve seatfacing uphole) and in that the flap 46 of the further cartridge 44 isprovided with a central aperture 48 extending therethrough. By virtue ofthe aperture 48, it will be understood that the flap 46 operates as anozzle within the body bore 18. In FIG. 1 of the accompanying drawings,the flap 46 is shown biased into engagement with the valve seat. Assuch, the flap 46 extends across the body bore 18 and providesresistance to fluid flowing downhole through the apparatus 2. However,fluid flowing uphole through the apparatus 2 will displace the flap 46and pass through the body bore 18 relatively unimpeded.

A spring 50 is located in a spring chamber 52 defined between a downholeportion of the mandrel 38, the downhole end of the uphole body component12 and an uphole portion of the downhole body component 14. The spring50 is compressed within the chamber 52 so as to press upwardly on thedownhole end of the uphole body component 12 and downwardly on themandrel 38. The mandrel 38 is thereby biased downhole relative to thebody 4. As a consequence, the mandrel 38 presses against the furtherflapper cartridge 44 which in turns presses against the annular block42. The spring bias is not however of sufficient magnitude to shear theshear pins 40. As will be explained hereinafter, the shear pins 40 aresheared by selectively increasing the rate of fluid flow downholethrough the bore 18 and the aperture 48.

A cylindrical tungsten carbide stinger 54 is secured to, and extendsupwardly from, the downhole crossover member 10. The outer diameter ofthe stinger 54 is less than the inner diameter of the annular block 42,the body of the further flapper cartridge 44 and a lower portion of themandrel 38 so as to allow these components to move downwardly betweenthe stinger 54 and the downhole body component 14 once the shear pins 40have been sheared (see FIGS. 2 to 4). When the apparatus 2 is configuredfor running in hole (see FIG. 1), the uphole end of the stinger 54 islocated uphole of the annular block 42 but downhole of the valve seat ofthe further flapper cartridge 44 so as to avoid hindering a sealingengagement of the flap 46 with said valve seat. The inner diameters ofthe stinger 54, the upper portion of the mandrel 38 and the uphole anddownhole crossover members 8,10 are approximately the same so as tominimise losses through the apparatus 2.

In use, the downhole valve 2 will be typically run downhole as part of acleaning string. The valve 2 will be run in the configuration shown inFIG. 1. In other words, the valve 2 is run with the mandrel 28 locatedin the uphole position so that the one-way valve assembly 6 is renderedinoperable (i.e. incapable of restricting fluid flow through theapparatus bore 18). The lower flapper cartridge 44 is neverthelessoperable and will tend to oppose fluid flowing downhole through thevalve 2. As the cleaning string is run in hole, wellbore fluid may draininto the valve 2 from the downhole end thereof and, in so doing, mayrotate the flap 46 upwardly against the spring bias associated with saidflap. Once the cleaning string is in a required position, the wellboreannulus may be flushed by pumping fluid down the annulus and upwardlyvia the bore extending longitudinally through the cleaning string. Thislongitudinal bore includes the bore 18 of the valve 2 and it will beappreciated that the ability of the flap 46 to hinge upwardly ensuresthis upward flow is not unduly resisted.

If polluting materials such as oil deposits are recovered at thesurface, then any further migration of these materials to the surfacemay be prevented through activation of the one-way valve assembly 6.This activation is achieved by reversing the fluid flow and pumpingfluid downwardly through the bore 18. In turn, the flap 46 moves intoengagement with its associated valve seat (under the combined influenceof the downward fluid flow and associated spring bias). Thisconfiguration is shown in FIG. 1. The aperture 48 in the flap 46 allowsfluid to continue to flow down through the cleaning string, but the flap46 itself allows the fluid to generate a sufficient downward force onthe annular block 42 to shear the shear pins 40 (see FIG. 2). Once theshear pins 40 have been sheared, the mandrel 38, flapper cartridge 44and annular block 42 are pressed downhole by the compression spring 50.As will be seen with reference to FIG. 3, as the lower flapper cartridge44 is pressed over the stinger 54, the upper end of the stinger 54 abutsthe flap 46 and rotates said flap 46 against the associated spring bias.With reference to FIG. 4, it will be seen that as the mandrel 38 ispressed further downhole relative to the body 4, the flap 46 is rotatedthrough approximately 90° and locates in the annular space between thestinger 54 and the downhole body component 14. Also, as will be seenfrom FIG. 4, the downhole movement of the mandrel 38 results in theupper end thereof becoming spaced from the flaps 34 of the one-way valveassembly 6 to the extent that said flaps 34 are free to rotate undertheir associated spring bias through 90° and thereby engage with theirassociated valve seats 32. In this way, a subsequent migration of fluid(located downhole of the one-way valve assembly 6) upwardly passed saidassembly 6 to the surface is prevented. However, fluid may neverthelessbe pumped downhole via the bore 18. Such a downhole fluid flow is notobstructed by the lower flapper cartridge 44 since the flap 46 thereofis rendered inoperable by the stinger 54. Wellbore fluid is thereforefree to flow downwardly through the apparatus 2 and drain therefrom whenthe cleaning string is run out of hole.

The present invention is not limited to the specific embodimentdescribed above. Modifications and alternative materials will beapparent to a reader skilled in the art. For example, the flap 46 may beprovided without the aperture 48 so that the one-way valve assembly maybe activated with static fluid pressure.

A further modification provides means which actively locks the mandrel38 in the position shown in FIG. 4. This locking means is shown in FIGS.5 and 6 in deactivated and activated configurations respectively. Thelocking means comprises a resilient circlip 70 located in a groove 72define in the exterior surface of the lower end of the mandrel 38. Thearrangement of the circlip 70 and groove 72 is such that the body 4presses the circlip 70 against its inherent spring bias into the groove72. The locking means further comprises a circumferential groove 74provided in a portion of the interior surface of the body 4 locatedbelow the shear pins 40. The arrangement is such that, when the mandrel38 locates in the position shown in FIG. 4, the groove 72 in the mandrel38 aligns with the groove 74 in the body 4 allowing the circlip 70 toexpand radially and span both circumferential grooves 72, 74. In thisway, the mandrel 38 becomes locked to the body 4. As such, the flap 46becomes locked in the inoperable configuration. The downhole edge of thecirclip 70 is provided with a chamfer so as to allow the mandrel 38 tobe pressed downwardly passed the groove 74 during disassembly of theapparatus.

The downhole valve 2 shown in FIGS. 1-4 and as modified in FIGS. 5 and 6may be used in conjunction with a further downhole valve 80 shown inFIGS. 7 and 8 and/or a yet further downhole valve 100 shown in FIGS.12-14 of the accompanying drawings. The downhole valve 80 shown in FIGS.7 and 8 is also shown in FIGS. 9-11 connected to the uphole end of thedownhole valve 2 of FIGS. 1-4. The downhole valves 80,100 operate toselectively prevent an uphole flow of fluid through the apparatus whilstrunning in hole.

In respect of each of the two valves 80,100, two flapper cartridges82,84 are arranged with the flaps 86 thereof spring biased into anupwardly rotated position wherein each flap 86 extends perpendicularlyto the longitudinal axis of the valve so as to block a bore 87 extendinglongitudinally through the valve 80,100. In this way, each flap 86prevents an uphole flow of fluid through the apparatus. However, giventhat the flaps 86 may be pressed and rotated downwardly about a fulcrum88, a downhole flow of fluid is not necessarily prevented by the flaps86.

In each of the downhole valves 80,100, the two flapper cartridges 82,84are retained between uphole facing and downhole facing shoulders 89,90which extend into the bore 87 of a valve body 91. A mandrel 92 islocated uphole of the two flaps 86 and is movable in an axial directionwithin the bore 87. With reference to the accompanying drawings, it willbe understood that, in an uphole position within the bore 87, themandrel 92 is spaced from the flaps 86 so as to allow said flaps 86 toclose the bore 87 to an uphole flow of fluid. However, in moving axiallydownhole within the bore 87, the downhole end of the mandrel 92 pressesagainst each flap 86 in turn and rotates each flap 86 about theassociated fulcrum 88. The bore 87 of the valve body 91 is therebyopened and an uphole flow of fluid may pass through the valve 80,100 viaa bore of the mandrel 92. A chamber 93 is provided between an upholeportion of the mandrel 92 and the valve body 91. Apertures 94 areprovided in the body 91 so as to vent, in use, the chamber 93 to theannulus and thereby assist axial movement of the mandrel 92.

The two downhole valves 80,100 differ in that the second valve 100 maybe repeatedly cycled between configurations wherein the flaps 86 areoperative and inoperative whereas the first valve 80 can only be movedfrom a flap operative configuration (as shown in FIG. 7) to a flapinoperative configuration (as shown in FIG. 8) on a single occasion. Inthis regard, it will be seen with reference to FIG. 7 that the mandrel92 of the first valve 80 is retained in the uphole position within thebore 87 by means of a shear mechanism. In the embodiment of FIGS. 7 and8, the shear mechanism comprises a plurality of shear pins 95 extendingfrom the body 91 of the valve 80 into an uphole end of the mandrel 92.It should be noted that the shear pins 95 are arranged so as to shear,in use, prior to the shear pins 40 of an associated downhole valve 2 asshown in FIGS. 1-4. In other words, the arrangement is such that staticfluid pressure may be increased within apparatus comprising the valves2,80 so that the flaps 86 may be rendered inoperable before the flaps 34become operable on a subsequent increase of fluid pressure. It will beunderstood that, once the shear pins 95 of the valve 80 have sheared,the mandrel 92 is permitted to move axially from the position shown inFIG. 7 to the position shown in FIG. 8 (i.e. from a position in whichthe flaps 86 are operative to a position in which the flaps 86 areinoperative). In this latter position of the mandrel 92, a snap ring inthe form of a circlip 96 locates downhole of a downhole facing shoulder97 in the bore 87. Abutment of the circlip 96 against the shoulder 97locks the mandrel 92 in the position relative to the body 91 shown inFIG. 8.

The valve 80 shown in FIGS. 7 and 8 is shown in FIGS. 9-11 connected tothe valve 2 of FIGS. 1-4. In FIG. 9, the valve 80 is shown arranged asin FIG. 7 whilst the valve 2 is shown arranged as illustrated in FIG. 1.In FIG. 10, the valve 80 is arranged as shown in FIG. 8 whilst the valve2 is again arranged as illustrated in FIG. 1. In use, the valve 80 ismoved from the arrangement of FIG. 9 to that of FIG. 10 by increasingthe static fluid pressure within the bore 87. The geometry of themandrel 92 and the placement of seals between the mandrel 92 and thebody 91 ensures the portion of mandrel 92 defining the chamber 93 isexposed merely to annulus fluid pressure and this allows fluid withinthe bore 87 to apply a resultant downhole force to the mandrel 92. Theshear pins 95 may be thereby sheared. However, as noted above, the fluidconditions resulting in this shearing of the shear pins 94 do not resultin a shearing of the shear pins 40 of the lower valve 2. Nevertheless,once the flaps 86 of the upper valve 80 have been rendered inoperable soas to allow an uphole flow of fluid, fluid pressure may be furtherincreased and the shear pins 40 of the lower valve 2 sheared in order tothen prevent uphole fluid flow by means of the flaps 34 of lower valve 2(as shown in FIG. 11).

The downhole valve 100 shown in FIGS. 12-14 comprises latch means whichallows the mandrel 92 to be selectively retained in an uphole position(see FIG. 12) or a downhole position (see FIG. 14). When in the downholeposition, the mandrel is retained by the latch means against the upholebias of a compression spring 102. The compression spring 102 is locatedin a downhole part of the chamber 93 defined between the mandrel 92 andthe valve body 91. The mandrel 93 is, in use, moved downhole against thebias of the spring 102 by the action of fluid pressure on the mandrel92. In the embodiment shown in FIGS. 12-14, a flapper cartridge 104 issecured to the uphole end of the mandrel 92 so as to allow readymovement of the mandrel 92 by means of dynamic fluid pressure. The flap106 of the flapper cartridge 104 comprises an aperture so as to allow adownhole flow of fluid through the valve bore 87. The arrangement of theflapper cartridge 104 is such that an uphole flow of fluid through thevalve bore 87 may rotate the flap 106 upwardly into a position whichdoes not obstruct the bore 87. If circumstances allow, the flappercartridge 106 may be omitted or replaced with a conventional nozzleattached to the mandrel 92.

The means by which the mandrel 92 can be repeatedly latched comprises apin and groove control arrangement. More particularly, in the valve 100shown in FIGS. 12-14, two pins 108 are mounted diametrically oppositeone another to the valve body 91. The pins 108 extend radially inwardfrom the body 91 into an indexing groove 110 provided on the exteriorsurface of a cylindrical indexing sleeve 112. The indexing sleeve 112 islocated in an uphole part of the chamber 93 and is pressed upholeagainst a downhole facing shoulder of the mandrel 92 by the spring 102.A thrust bearing 114 is located at either end of the cylindrical sleeve112 so as to assist in a ready rotation of the sleeve 112 relative tothe mandrel 92, spring 102, and the valve body 91. It will be understoodthat, in an alternative embodiment, the pins 108 may be provided on theindexing sleeve 112 with the groove 110 provided in the valve body 91.

It will be understood that, as fluid pressure is applied to the mandrel92 and the mandrel 92 is moved axially downhole relative to the body 91,the pins 108 move within the indexing groove 110. As the mandrel 92moves from the uphole position shown in FIG. 12 to the downhole positionshown in FIG. 13, the pins 108 move within the groove 110 in such a wayas to rotate the sleeve 112. If fluid pressure is reduced, the mandrel92 may move from the position shown in FIG. 13 to the position shown inFIG. 14 under the action of the spring 102. This latter axial movementis relatively small and the flaps 86 are retained in an inoperativeconfiguration. The pins 108 again move within the groove 110 and thisgenerates a further rotation of the sleeve 112. However, it will beunderstood from FIG. 14 that the pins 108 locate in a portion of thegroove 110 which prevents movement of the mandrel 92 uphole without themandrel 92 first being moved downhole relative to the valve body 91. Thegroove 110 forms a closed loop. The loop is formed about thelongitudinal axis of the valve 100 and so the pins 108 may be repeatedlycycled through the entirety of the groove 110. This allows a repeatedcycling of the mandrel 92 between uphole and downhole positions in whichthe flaps 86 are operable and inoperable. A snap ring mechanism forlocking the mandrel 92 to the valve body 91 is not provided in thedownhole valve 100.

In use, the downhole valve 100 may be connected to the uphole end of thedownhole valve 2 shown in FIGS. 1-4 in a similar manner to thatdescribed in relation to downhole valve 80 of FIGS. 7 and 8. However, ingeneral, it is envisaged that the valve 100 will be used without theneed for the other valves 2,80.

The downhole valve 80,100 shown in FIGS. 7 and 8 and FIGS. 12-14comprise a plurality of seals 116 which prevent the flow of fluidbetween component parts. Also, the mandrel of the valve 80 shown inFIGS. 7 and 8 may be provided with a nozzle or a flapper cartridgewherein the flap comprises an aperture so as to allow ready movement ofthe mandrel with dynamic fluid pressure. It will also be understood thatthe three valves 2,80,100 shown in the accompanying drawings can, inpractice, be used on their own and independently of the other twovalves. Alternatively, the valves may be used in combination with eachother.

1.-18. (canceled)
 19. A downhole annulus flushing valve comprising: a body having a bore extending longitudinally therethrough; a one-way valve for allowing fluid to flow in a first direction through the bore and preventing fluid flow in a second direction through the bore, the second direction being opposite to the first direction; means for rendering the one-way valve inoperable so as to be ineffective at preventing fluid flow; a one-way flow restrictor which permits substantially unrestricted flow through the body in the second direction and restricts flow through the body in the first direction; and means for selectively making the one-way valve operable so as to be effective at allowing fluid flow in said first direction and preventing fluid flow in said second direction.
 20. A downhole annulus flushing valve according to claim 19, wherein the means for selectively making the one-way valve operable is also effective to disable the one-way restrictor so that it permits substantially unrestricted flow through the body.
 21. A downhole tool as claimed in claim 19, wherein the means for rendering the one-way valve inoperable comprises means for restricting movement of said valve.
 22. A downhole tool as claimed in claim 21, wherein said movement restricting means is movable relative to the tool body and is biased towards a position wherein movement of the one-way valve is not restricted so as to render said valve inoperable.
 23. A downhole tool as claimed in claim 21, wherein said means for selectively making the one-way valve operable comprises said one-way flow restrictor.
 24. A downhole tool as claimed in claim 23, wherein the one-way flow restrictor is mounted on said movement restricting means with a pivotal connection so that the one-way flow restrictor tends to be moved to the first position by a fluid flowing through the tool bore in said first direction.
 25. A downhole tool s claimed in claim 23, wherein means are provided for retaining the one-way flow restrictor in the second position when said movement restricting means is in a position wherein movement of the one-way valve is not restricted so as to render said valve inoperable.
 26. A downhole tool as claimed in claim 23, wherein the closure member is biased towards the second position.
 27. A downhole tool as claimed in claim 21, wherein said means for selectively making the one-way valve operable comprises means for releasably retaining said movement restricting means in a position wherein the one-way valve is inoperable.
 28. A downhole tool as claimed in claim 27, wherein said means for releasably retaining said movement restricting means comprises a shear pin securing said movement restricting means to the tool body.
 29. A downhole tool as claimed in claim 27, wherein said means for releasably retaining said movement restricting means comprises a latching means.
 30. A downhole tool as claimed in claim 29, wherein said latching means comprises a pin mounted to one of the tool body and movement restricting means; and a groove, for receiving the pin, mounted in the other of the tool body and movement restricting means.
 31. A downhole tool as claimed in claim 30, wherein the groove defines a closed loop.
 32. A downhole tool as claimed in claim 1, wherein the one-way valve comprises a closure member pivotally mounted to the tool body and movable between a first position in which fluid within the body bore may flow passed the closure member, and a second position in which fluid within the body bore is prevented from flowing past the closure member so that fluid on one side of the closure member is isolated from fluid on an opposite side of the closure member. 